The success of many normal immune responses require the participation of T-cells. The proliferation of T-cells to sufficiently large numbers to enable them to assume an effective role in immune responses is controlled by the presence of the polypeptide growth hormone interleukin 2 (hereinafter "IL-2"), formerly known in the literature as "T-cell growth factor" or "TCGF." Gillis and Smith, 28 Nature 154 (1977). The mechanism by which IL-2 controls the growth of T-cells is not completely understood. However, it is known that IL-2 acts on T-cells via a specific, high affinity plasma membrane receptor. Also, in order to continue to divide, IL-2 dependent T-cells must express this receptor and IL-2 must bind to a portion of this receptor. Robb et al., 154 J. Exp. Med. 1455 (1981). A more complete knowledge of the biochemistry of the IL-2 receptor would foster a better understanding of the interaction between IL-2 and T-cells. To date, this has been hampered, at least in part, by the unavailability of IL- 2 receptor in purified form.
Leonard et al., 300 Nature (London) 267 (November 1982), reported employing a murine monoclonal antibody, designated as anti-Tac, to significantly block the binding of radiolabelled IL-2 to the human lymphoma T-cell line, HUT-102. This antibody resulted from the immunization of mice with long term cultures of human T-cells. The anti-Tac antibody was reported as binding to a glyco-protein receptor having a molecular weight of about 47,000-53,000 daltons and also to proteins having molecular weights of about 113,000 and 180,000 daltons. Leonard et al. hypothesized, but did not establish, that the cell surface determinant (i.e., the 47,000-53,000 molecular weight protein) to which the anti-Tac antibody bounded to was the IL-2 receptor.
Robb and Green, 158 J. Exp. Med. 1332 (1983), reported employing the anti-Tac antibody in conjunction with mitogen-activated normal lymphocytes to immunoprecipitate a protein having a molecular weight of about 52,000-57,000 daltons. They found that this same protein also bound to IL-2. These researchers opined that this reactive molecule contained the binding site for IL-2 for normal lymphocytes.
Leonard et al., 80 Proc. Natl. Acad. Sci. (U.S.A.) 6957 (1983) observed that receptors recognized by anti-Tac antibody on HUT-102 cells and on phytohemaggelutinin-activated normal T-cells appear to be larger on reducing gels than on nonreducing gels, thus suggesting the presence of intrachain disufide bonds. Also, the HUT-102 cell receptor was reported to exhibit an isoelectric point of from 5.5 to 6.0. From post-translational studies Leonard et al. suggested that the HUT-102 receptor is composed of a peptide backbone of 33,000 molecular weight that is initially glycosylated by an N-linked mechanism to achieve a 35,000-37,000 molecular weight doublet and then glycosylated by an O-linked mechanism to increase the weight of the molecule by about 13,000-15,000 datons. Although the researchers stated that their studies "suggested" that the HUT-102 cell receptor recognized by the anti-Tac antibody is the human receptor for IL-2, they admitted that actual proof would require purifying the receptor, which prior to the making of the present invention had not been accomplished.